As is well known in the automobile industry, electric vehicles (EV) and hybrid-electric vehicles (HEV) may be provided with one or more high voltage batteries for powering the vehicle drivetrain. Such batteries require periodic re-charging after depletion, which may be accomplished by connecting the vehicle to a high voltage AC power line, which may be 120 or 240 volt AC, supplied by an electric utility grid. Such a connection may utilize a suitable vehicle connector configured to interface with a vehicle on-board battery charger (OBC).
Electric and hybrid-electric vehicles may also include a low voltage battery, such as a 12 volt DC battery, for powering low voltage vehicle electrical systems and circuitry. Some or all of such electrical systems and/or circuitry of an EV or HEV could be supplied with energy from a high voltage power source when the vehicle is connected to an AC power line. In that event, such a power source is virtually unlimited and such an arrangement would help preserve the charge and/or extend the life of the vehicle 12 volt DC battery. In the absence of the vehicle connection to the AC power line, certain control circuitry could be supplied with sufficient power from the vehicle 12 volt DC battery to perform various diagnostic functions and/or to permit reprogramming of that control circuitry, such as re-flashing for software updates.
Such an arrangement, however, requires switching between the high voltage power source and the vehicle 12 volt DC battery, depending upon the presence or absence of the vehicle connection to the high voltage AC power line. Such switching may be accomplished using control circuitry and suitable components to sense or detect the presence of the high voltage power. The use of such control circuitry and sensing components, however, adds cost to the EV or HEV and necessarily increases the possibility of circuitry, component and/or system failures.
As a result, there exists a need for multistage power supply system and method for providing uninterrupted low voltage electrical power to control circuitry in an EV or HEV. Such a multistage power supply system and method would be dual source, accepting energy from a high voltage power source and a low voltage vehicle battery. Such a multistage power supply system and method would provide low voltage power for vehicle control circuitry from the high voltage power source when the high voltage power source is present as a result of a connection of an EV or HEV to a high voltage AC power line, and would provide such low voltage power from the low voltage vehicle battery when the high voltage power source is absent. Such a multistage power supply system and method, which could be implemented as part of a vehicle OBC, would do so without control circuitry for switching between the high voltage power source and the low voltage vehicle battery and with a minimal number of components in order to reduce cost and improve reliability.